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Nature of Electromagnetic Waves is considered one the most difficult concept.
78 Questions around this concept.
In an electromagnetic wave, at an instant and at a particular position, the electric field is along the negative z axis and magnetic field is along the positive x-axis. Then the direction of propagation of electromagnetic wave is :
Nature of Electromagnetic Waves
From Maxwell’s equations, we can observe that electric and magnetic fields in an electromagnetic wave are perpendicular to each other, and to the direction of propagation. Also from our discussion of the displacement current, in that capacitor, the electric field inside the plates of the capacitor is directed perpendicular to the plates. The figure given below shows a typical example of a plane electromagnetic wave propagating along the z direction (the fields are shown as a function of the z coordinate, at a given time t). The electric field Ex is along the x-axis, and varies sinusoidally with z, at a given time. The magnetic field By is along the y-axis, and again varies sinusoidally with z.The electric and magnetic fields Ex and By are perpendicular to each other, and to the direction z of propagation.
Now from the Lorentz equation -
since, , where f is the frequency and , where is the wavelength.
But gives the velocity of the wave. So, . So we can write -
It is also seen from Maxwell’s equations that the magnitude of the electric and the magnetic fields in an electromagnetic wave are related as -
In a material medium of permittivity ε and magnetic permeability µ, the velocity of light becomes,
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